I definitely agree with Ben here -- a UV filter is a very good idea for use in the desert. As for which filters to use, you are probably best off thinking about the color principles. A filter lightens the color that is appears to your eye, and darkens the complimentary color. So if you have a scene with blue sky, white clouds and orange sand, and orange filter would darken the sky, increase the contrast, and lighten the orange sand. On the other hand, a blue filter would darken the sand, lighten the sky (and lower the contrast in the sky...probably washing it out).
One way to decide which filter to bring is pretty easy if you have photoshop.
Step 1: Find some color pictures of the places you plan on visiting.
Step 2. Save them to your desktop (delete them when you are done if they are not open use images).
Step 3. Open photoshop and run the "photo filter" utility in the adjustment menu.
Step 4. Apply whatever color filter you feel like trying.
Step 5. Convert the image to grayscale.
That will allow you to see the effect of the filter on the scenes that you plan on photographing! As for filters, I would spring for the B+W MRC filters...they are just better. The brass rings make them easy to get on and off, and their coating not only prevents almost all flare and ghosting, it actually sheds dirt, fingerprints and so on. They are really worth it, especially if you plan to be using high quality rangefinder lenses. It's another thing if you are using a 4-4000mm consumer zoom...